Low concentration of bromide ions improves sulfadiazine phytoremoval and attenuates its phytotoxicity

Sulfonamide antibiotics (SAs) are ubiquitous in surface water and soil environments, raising considerable concerns about their risk and removal. However, the impacts of various bromide ion (Br^-) concentrations on the phytotoxicity, uptake and fate of SAs in plant growth and physiological metabolism of plants have not been well understood. Our research demonstrated that low concentrations of Br^- (0.1, 0.5 mM) promoted the uptake and degradation of sulfadiazine (SDZ) in wheat and attenuated the phytotoxicity of SDZ. Additionally, we proposed a degradation pathway and identified the brominated product of SDZ (SDZ^Br), which attenuated the dihydrofolate synthesis inhibition by SDZ. The primary mechanism was that Br^- reduced the level of reactive oxygen radicals (ROS) and alleviated oxidative damage. The production of SDZ^Br and the high consumption of H₂O₂ suggest the potential generation of reactive bromine species, contributing to the degradation of the electron-rich SDZ and thus reducing its toxicity. Moreover, metabolome analysis of wheat roots indicated that low concentrations of Br^- stimulated the production of indoleacetic acid under SDZ stress, promoting growth and enhancing the uptake and degradation of SDZ. Conversely, high Br^- (1 mM) concentration produced a deleterious effect. These findings provide valuable insights into the mechanisms of antibiotic removal, suggesting a potentially novel approach to plant-based antibiotic remediation.